Polyhalogenated hydrocarbons and in particular the polychlorobiphenyls are substances widely employed in industry for their useful properties, including their considerable stability upon heating and pressure application.
Such substances are nevertheless very toxic for the flora and fauna, and their leakage into the soil may lead to serious environmental risks. It has already occurred that, following the accidental outflow of PCBs and their degradation products, such as polychlorodibenzodioxins (PCDDs) and polychlorodibenzofurans (PCDFs) from plants for the production of polyhalogenated hydrocarbons (for example insecticides), access has been prohibited to even quite vast land areas, also in urban environments.
Different methods of remediating soils contaminated by PCBs and/or PCDDs and PCDFs have been proposed, some based on chemical reactions (see for example U.S. Pat. No. 5,197,823 and US 2002143226) conducted on the soil, others based on the absorption by a polymeric support after grinding the soil and admixing it with water and with the aforementioned support (see FR 2 797 598), still others based on treatments with solvents (U.S. Pat. No. 4,801,394).
These methods are quite complicated and costly from the standpoint of both plant design and energy consumption. Moreover, such methods do not lend themselves to being carried out in place but require the removal of the contaminated soil and its transportation by trucks to the remediation plant.
U.S. Pat. No. 5,658,094 discloses a system for remediating soil contaminated with hydrocarbons and PCB's, which system includes a rotary drum having first and second heat exchanging regions, each containing separated inner and outer regions. The drum is inclined so that the fed soil is gravitationally urged through the inner regions, whereas thermal energy provided by burner means remediates the soil by vaporizing and oxidizing the hydrocarbons and PCB's in a stream of hot gases. Temperatures as high as 2000° F. (1093° C.) are reached.
EP-A-1 170 067 discloses a method of remediating soil that contains heavy metals, comprising the step of treating a sieved soil in a thin layer, kept in a strongly turbulent state, with a solution of an alkali sulfide at a temperature of at least 50° C.
U.S. Pat. No. 6,213,030 describes an apparatus for the treatment volatile materials in contaminated materials including a retort assembly which includes a rotatable retort disposed at least partially within a combustion chamber with a heater to indirectly heat the contents of the rotatable retort.